The Bishop's Sword

When Detective-Inspector Lancelot Carolus Smith finds a puzzling case he seems to find three of them at a time. This time, all three are real puzzlers. (1) How did someone steal the priceless Bishop’s Sword from the hermetically sealed glass case? (2) How did a man who was in jail visit a police official at night at his home? And (3) how did seven men enter the one-exited cave and only six come out?